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Date: Sat, 22 Dec 2012 03:09:29 +0000
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Subject: Re: Intermittent failures retrieving process exit codes
From: Nick Lowe <nick.lowe@gmail.com>
To: Andrey Repin <cygwin@cygwin.com>
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The documentation in MSDN is incorrect/incomplete with regards to
TerminateThread/TerminateProcess, both are definitely asynchronous.

I am not clear/confident on the behaviour of ExitProcess and
ExitThread, but will investigate with IDA and a test case later. I
suspect any locking/serialisation will pertain to these functions
only.

On Fri, Dec 21, 2012 at 7:44 PM, Tom Honermann <thonermann@coverity.com> wrote:
> On 12/21/2012 07:15 AM, Nick Lowe wrote:
>>
>> Briefly casting my eye at the test case, as a general point, remember
>> that these termination APIs all complete asynchronously and I do not
>> believe it has ever been safe or correct to call another while one is
>> still pending - you are in undefined, edge case behaviour territory
>> here.
>
>
> These comments do not match my understanding of these APIs.  MSDN
> documentation contradicts some of this as well.
>
>
>> Win32's TerminateThread/ExitThread, that in turn calls the native
>> NtTerminateThread, only requests cancellation of a thread and returns
>> immediately.
>> One has to wait on a handle to the thread know that termination has
>> completed, for which the synchronise standard access right is
>> required.
>> The same is true of Win32's TerminateProcess/ExitProcess, in turn
>> NtTerminateProcess, where one waits instead on a handle to the
>> process.
>
>
> TerminateProcess() is documented to perform error checking and then to
> schedule asynchronous termination of the specified process.  I would not be
> surprised if the asynchronous termination applies even when
> GetCurrentProcess() is used to specify the process to terminate, but I would
> likewise not be surprised if TerminateProcess() has special handling for
> this.  I agree that calls to TerminateProcess() might return before the
> calling thread/process is terminated.  I have not tried to verify this
> behavior though.
>
> http://msdn.microsoft.com/en-us/library/windows/desktop/ms686714%28v=vs.85%29.aspx
>
> The MSDN documentation for TerminateThread() does not state that the
> termination is carried out asynchronously, but I would not be surprised if
> that is the case.
>
> http://msdn.microsoft.com/en-us/library/windows/desktop/ms686717%28v=vs.85%29.aspx
>
> I would be *very* surprised if it is possible for ExitProcess() and
> ExitThread() to return (unless the thread is being suspended and its context
> manipulated by another process/thread).  The MSDN docs for these do not
> mention any possibility of return.  In addition, the ExitThread()
> documentation explicitly states that Windows manages serialization of calls
> to ExitProcess() and ExitThread().
>
> <quote>
> The ExitProcess, ExitThread, CreateThread, CreateRemoteThread functions, and
> a process that is starting (as the result of a CreateProcess call) are
> serialized between each other within a process. Only one of these events can
> happen in an address space at a time.
> </quote>
>
> http://msdn.microsoft.com/en-us/library/windows/desktop/ms682659%28v=vs.85%29.aspx
>
> http://msdn.microsoft.com/en-us/library/windows/desktop/ms682658%28v=vs.85%29.aspx
>
> I read that quote as supporting my assertion that the observed behavior is a
> defect in Windows.  It appears Windows is failing to serialize the calls
> appropriately.
>
> Tom.
>
>
>
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